Various forms of brachytherapy have been practiced since the time of discovery of radioactivity by Mme. Curie. Brachytherapy, from the Greek root meaning “from a short or near distance” is a term typically used to describe the placement of one or more radioactive sources within tissue or in a body lumen or body cavity to deliver a therapeutic dose to a tumor or tumor bed near the source. Brachytherapy as it is practiced today includes several varieties of invasive treatment. Interstitial brachytherapy includes the step of placing the radioactive source or sources within the tissue (e.g. prostate gland). Intra-luminal brachytherapy includes introducing the source through an anatomical lumen (e.g. vascular). Intra-cavitary brachytherapy is performed by placing the radioactive source inside a naturally occurring cavity near the cancerous tissue (e.g. cervical cancer, or orbital cavity for intra-ocular melanoma), or a man-made cavity created during surgery (e.g. breast lumpectomy or other tumor beds). Various brachytherapy applicators are known and used in invasive procedures.
A surface applicator, including structure for defining a series of parallel lumens for receiving high dose radiation (HDR) sources, has been used for treatment of surface lesions, skin cancer or during open surgeries for tissues which are easily accessed. (See, for example, the Varian catalog at www.varian.com/obry/pdf/vbtapplicatorcatalogue.pdf, page 113). This applicator is not designed to treat a deep seated tumor or tumor bed, however.
Cash et al. (U.S. Pat. No. 6,560,312) discloses a technique of performing radiosurgery on a human body using teletherapy. The technique includes accumulating non-converging radiation fields to reach a therapeutic dose. The teletherapy design of Cash et al. is based upon a predetermined distribution of remote x-ray sources to create a volume where multiple beams intersect within the human body. It relies on the ability to align remote sources located on one platform to treat a lesion within a patient who is positioned on a separate platform. This approach has major limitations where relative positioning of the sources must be carefully maintained in order to provide precise lesion tracking, particularly when patient motion, such as that associated with breathing, can cause misalignments during treatment (as for example, when the patient is being treated for breast cancer).
Sundqvist (U.S. Pat. No. 4,780,898) and Leskell (U.S. Pat. Nos. 5,528,651, 5,629,967 and 6,049,587) collectively describe a teletherapy system sold under the trademark “GammaKnife”, and assigned to Elekta Instrument AB. The system is used to treat inoperable fine brain tumors by exposing a localized point within the brain of the patient. Gamma Knife relies on rigidly immobilizing the head of a patient by attaching a “helmet” directly to the skull, and simultaneously exposing the brain tissue to sources of radiation from multiple angles. Each source is collimated, emitting converging radiation beamlets that target a single focus point. By careful alignment of each of the source beamlets or lines of treatment, the Gamma-Knife system is able to build up the radiation field to therapeutic levels at the location of the target. The design is useful for treatment of very fine (point) lesions and requires careful orientation of each beamlet or line of treatment.